Apparatus and method for dynamic diversity based upon receiver-side assessment of link quality

ABSTRACT

An apparatus for dynamic diversity signal reception based upon receiver-side link quality assessments includes two or more antennae. At least one switch is connected to the two or more antennae. A dynamic diversity controller is connected to the at least one switch. The dynamic diversity controller includes a link quality assessor to assess link quality and generate a link characterization value. A diversity configuration selector, responsive to the link characterization value, selectively activates the at least one switch to implement a dynamic diversity configuration. The link quality assessor includes a signal strength analyzer, a modem detector, and/or a MAC layer analyzer to assess the received signal and generate the link characterization value.

[0001] This application claims priority to U.S. provisional patentapplication serial No. 60/355,266, filed Feb. 9, 2002, the entirecontent of which is incorporated herein by reference.

BRIEF DESCRIPTION OF THE INVENTION

[0002] This invention relates generally to wireless signal processing.More particularly, this invention relates to dynamic diversity selectionbased upon receiver-side link quality assessments.

BACKGROUND OF THE INVENTION

[0003] Diversity is a form of signal reception in which the outputsignals from two or more independent antennae are combined to provide asignal that is less likely to fade. Various diversity schemes are knownin the art. By way of example, various diversity schemes will bediscussed in connection with two receive antennae. Each of thesediversity schemes is equally applicable to multiple receive antennae.

[0004] When there is only one antenna there is no diversity. A nodiversity configuration allows for the simplest implementation andresults in the lowest power consumption. On the other hand, in theabsence of a diversity configuration, the received signal is vulnerableto fading.

[0005] In a switched diversity scheme, only one antenna is chosen at anygiven time during reception. The choice is based on some prescribedselection criterion. The antenna connection is switched when theperceived link quality falls below a certain prescribed threshold.

[0006] In a selection diversity scheme, the antenna with the largestsignal-to-noise ratio (SNR) or signal power is utilized. The SNR orsignal strength measurement can take place during a preamble period atthe beginning of a received packet. In this scheme, a single antennaconnection is maintained at most times, but both antennae connectionsare utilized while the SNRs or signal strengths are measured. The actualselection/switching process can take place between packet receptions.The selection process can be done on a packet-by-packet basis or cantake place once in a number of receptions or during a prescribed timeperiod.

[0007] In a full diversity scheme, both antennae are connected at alltimes. This mode consumes the largest power as both received paths mustbe powered up, but also offers the largest performance gain, especiallyin severe fading environments with large delay spread, compared to otherconfigurations.

[0008] In sum, there are various advantages and disadvantages associatedwith each prior art diversity scheme. These advantages and disadvantagesrelate to tradeoffs between the quality of the signal reception and theamount of power consumed. For mobile wireless communication devicesthere are continuing pressures to reduce power consumption. Thus, itwould be highly desirable to identify a technique for dynamicallyselecting a diversity configuration while optimizing signal receptionand reducing power consumption.

SUMMARY OF THE INVENTION

[0009] An apparatus for dynamic diversity signal reception based uponreceiver-side link quality assessments includes two or more antennae. Atleast one switch is connected to the two or more antennae. A dynamicdiversity controller is connected to the at least one switch. Thedynamic diversity controller includes a link quality assessor to assesslink quality and generate a link characterization value. A diversityconfiguration selector, responsive to the link characterization value,selectively activates the at least one switch to implement a dynamicdiversity configuration. The link quality assessor includes a signalstrength analyzer, a modem detector, and/or a MAC layer analyzer toassess link quality and generate the link characterization value.

[0010] The invention also includes an apparatus to facilitate dynamicdiversity signal reception. This apparatus has a bus, a control circuitconnected to the bus, and input and output devices connected to the busto route received link information and transmit control signals. Adynamic diversity control module is also connected to the bus. Thedynamic diversity control module has a link quality assessor and adiversity configuration selector. The link quality assessor implementsalternate or cumulative strategies to process the received linkinformation and generate a link characterization value. Based upon thelink characterization value, the diversity configuration selectoractivates a diversity configuration.

[0011] The invention also includes a method of dynamic diversityselection based upon receiver-side link quality assessments. The methodincludes receiving link information at a wireless mobile device. Thelink information is assessed using a technique selected from a signalstrength analysis, a modem detection analysis, and a medium accesscontrol (MAC) analysis. An antenna diversity configuration is selectedbased upon the assessment of the link information.

[0012] There are a number of advantages associated with the technique ofthe invention. First, since the technique of the invention isimplemented at the receiver, it does not interfere with traditionaltransmitter-side link-enhancing techniques, such as transmitter powercontrol and packet retransmission. Second, the dynamic diversitytechnique of the invention allows the communication system tosignificantly enhance its ability to maintain a reliable link in adversechannel conditions without sacrificing the data transfer rate. Thetechnique also allows a receiver to operate at an improved data rateunder a given channel condition, compared to the conventional switcheddiversity, selection diversity or non-diversity configurations. Thetechnique of the invention facilitates the consumption of considerablyless power than a full diversity implementation without a significantsacrifice in throughput. Advantageously, the dynamic mode selectiontechnique of the invention can utilize various physical (PHY) layer aswell as medium access control (MAC) layer parameters to identify achange in the quality of the communication link.

BRIEF DESCRIPTION OF THE FIGURES

[0013] The invention is more fully appreciated in connection with thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

[0014]FIG. 1 illustrates a model of a wireless channel.

[0015]FIG. 2 illustrates a model of a wireless channel with two receiveantennae.

[0016]FIG. 3 illustrates a diversity configuration selection routinewith full diversity and switched diversity modes in accordance with anembodiment of the invention.

[0017]FIG. 4 illustrates a diversity configuration selection routinewith full diversity and no diversity modes in accordance with anembodiment of the invention.

[0018]FIG. 5 illustrates a diversity configuration selection routineutilized in accordance with an embodiment of the invention.

[0019]FIG. 6 illustrates a link quality assessor, diversityconfiguration selector, and switch configuration utilized in accordancewith an embodiment of the invention.

[0020]FIG. 7 illustrates a link quality assessor, diversity selectioncontroller, and switch configuration utilized in accordance with analternate embodiment of the invention.

[0021]FIG. 8 illustrates an embodiment of a dynamic diversity controllerwith a link quality assessor and a diversity configuration selectorutilized in accordance with an embodiment of the invention.

[0022] Like reference numerals refer to corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Consider the representative quadrature amplitude modulation (QAM)system depicted in FIG. 1. The received sample r_(k) is given by

r _(k) =g _(k) A _(k) +n _(k)  (1)

[0024] where g_(k) represents the fading in the wireless medium, A_(k)is the QAM symbol and n_(k) is the additive noise. All variables arecomplex-valued in general. This is a general description of QAM symbolsbeing transmitted over a fading channel corrupted by additive noise. Assuch, equation (1) can be either a time-domain or a frequency-domainmodel. In a practical wireless system that utilizes a finite number, sayN, fixed frequency bins, the model of equation (1) is applied with anunderlying assumption that the k-th symbol transmission occupies the (kmodulo N)-th frequency bin. Bins are used in a successive manner fromthe first bin to the last one, and then back to the first one and so on.Among specific examples of the latter system are frequency divisionmultiplexing (FDM) and orthogonal frequency division multiplexing (OFDM)systems.

[0025] Now consider the channel model of FIG. 2 that results from theuse of one transmit antenna and two receive antennae. Extensions tomultiple channels corresponding to multiple receive antennae and,possibly, multiple transmit antennae are straightforward to anyoneskilled in the art. For standard-compliant applications such as wirelesslocal area network (WLAN), compatibility with a basic transceiver/modemdesign must be ensured. For this reason, no transmit antenna diversityis assumed in this invention. The received samples for the two antennaeare given by

r _(l,k) =g _(l,k) A _(k) +n _(l,k)  (2a)

r _(2,k) =g _(2,k) A _(k) +n _(2,k)  (2b)

[0026] where the double subscript is used for the channel fade parameterand noise to distinguish between the two receive paths. Also shown inFIG. 2 is the bit-to-symbol mapping block, which converts a fixed numberof bits into a QAM symbol and the nonlinear processor that producesdecisions on the transmitted bits {circumflex over (b)}_(k). Thesedecisions can be either hard or soft. Various prior art implementationsexist for this nonlinear processor.

[0027] In the context of the models of FIGS. 1 and 2, the presentinvention facilitates the dynamic and automatic selection of thereceiver antennae diversity mode based on link quality assessment. In aconventional indoor WLAN, for example, the data rate of a givencommunication link is typically adjusted at the transmitter-side basedon some measure of the successful packet transmission rate. As thechannel condition gets worse (e.g., as the receiving station moves awayfrom the transmitting station, or the antenna orientation changes in amobile station), the link data rate is adjusted down to a lower rate, asthe reliable communication at the initial rate is no longer feasible.Dynamic diversity enables a higher link rate in more adverse channelconditions than is possible in conventional systems, while avoidingexcessive overall power consumption by the transceiver/modem components.In contrast to the conventional WLAN system based on transmitter-sidelink quality assessment, dynamic diversity requires a receiver-side linkquality measure.

[0028]FIG. 3 is a state transition diagram illustrating dynamicdiversity control in accordance with an embodiment of the invention.This embodiment allows dynamic diversity selection between the low powerswitched diversity mode and the high performance, full diversity mode.Observe in FIG. 3 that each antenna can alternately operate in aswitched diversity mode and a full diversity mode.

[0029]FIG. 4 is a state transition diagram illustrating dynamicdiversity control in accordance with an alternate embodiment of theinvention. This embodiment allows dynamic transition between fulldiversity and no diversity. As the link quality deteriorates, thereceiver transitions from a single antenna connection to the fulldiversity mode. The transition back to a single antenna connection istriggered by an indication of significantly improved link quality. Whengoing back to a single antenna configuration, comparison of the receivedsignal strengths in the two antennae paths leads to a preferable antennaconnection. In this sense, the scheme of FIG. 4 also incorporates a“slow” form of selection diversity.

[0030]FIG. 5 is a flow chart description of the dynamic diversitycontroller depicted in FIG. 4. RLQM stands for the receiver-side linkquality measure and RSSI is the receive signal strength indicator. Ifthe RLQM at the first antenna is greater than or equal to a firstthreshold (TH1), then the connection is maintained at the first antenna(block 500). Similarly, if the RLQM at the second antenna is greaterthan or equal to the first threshold (TH1), then the connection ismaintained at the second antenna (block 502).

[0031] If the RLQM is beneath the first threshold (TH1), then the fulldiversity mode is entered at block 504. This mode is maintained as longas the RLQM is beneath a second threshold (TH2). When the RLQM isgreater than or equal to the second threshold (TH2), then a decision ismade at block 506. If the receive signal strength indicator for thefirst antenna (RSSI1) is greater than the receive signal strengthindicator for the second antenna (RSSI2), then control proceeds to block500, otherwise control proceeds to block 502.

[0032] In an effort to reduce power consumption further, the fulldiversity mode can be disabled at the end of packet reception and untildetection of a new packet. As soon as the arrival of a new packet isdetected, full diversity can resume, unless the most recent link qualitymeasure indicates a sufficient margin and thus suggests switching to thelow power antenna mode.

[0033] As shown in FIG. 5, transition between diversity modes and/orantennae connections is signaled by a change in the perceived linkquality level. The transmit-side link quality assessment is typicallybased on the estimated dropped packet rate via the observation of theacknowledgement packet and the number of retries attempted. However, thelink quality assessment at the receiver-side, as required for dynamicdiversity, must rely on different methods. Receiver-side link qualityassessment may be performed using various techniques associated with theinvention. In particular, the invention can utilize a signal strengthanalyzer, a modem detector, and/or a MAC layer analyzer to performreceiver-side link quality assessment, as discussed below.

[0034] In accordance with an embodiment of the invention, a signalstrength analyzer assesses received signal strength (RSS). RSS is ameasure of the average signal power and is relatively easy to estimate.The RSS signal can be combined with a measure of delay spread ormulti-path interference to provide an accurate link quality estimate. InOFDM the coherence bandwidth (the reciprocal of the delay spread) of themulti-path channel can be measured from the frequency correlationfunction that is approximated as $\begin{matrix}{\varphi_{n} = \frac{\left. {\frac{1}{N - n}\sum\limits_{k = {n + 1}}^{N}}\quad \middle| {H_{k}{\left. H_{k - n} \right|}} \right.}{\left. {\frac{1}{N}\sum\limits_{k = 1}^{N}}\quad \middle| H_{k} \right|^{2}}} & (3)\end{matrix}$

[0035] where H_(k) represents the frequency response of the channel andN is the total number of subcarriers. The 50% coherence bandwidth,denoted as B₅₀, can be defined as the width of this frequencycorrelation function at 50% of the peak. The rms delay spread is roughlyapproximated as $\begin{matrix}{\tau_{rms} \approx {\frac{1}{5B_{50}}\quad.}} & (4)\end{matrix}$

[0036] A simpler way of estimating the coherence bandwidth is to look atthe overall deviation of the frequency response from an average value.For example, one can compute $\begin{matrix}{{\sum\limits_{k = 1}^{N}\quad {\left\lbrack \left| H_{k} \middle| {- S} \right. \right\rbrack^{2}/S^{2}}}{or}} & (5) \\\left. {\sum\limits_{k = 1}^{N}\quad \left. ||H_{k} \right.} \middle| {- S} \middle| {/S} \right. & (6)\end{matrix}$

[0037] where S=(1/N)Σ_(k=1) ^(N)|H_(k)|. The delay spread can also beestimated by measuring the accumulated differences of the adjacenttones. For example, the rms delay spread can be related to$\begin{matrix}\left. {\sum\limits_{k = {L + 1}}^{N}\quad \left. ||H_{k} \right.} \middle| {}_{2}{- \left| H_{k - L} \middle| {}_{2} \middle| {/\sum\limits_{k = 1}^{N}}\quad \middle| H_{k} \middle| {}_{2}, \right.} \right. & (7)\end{matrix}$

[0038] where L is 1 or a small positive integer. The denominator of (7)is simply a constant and thus can be ignored under a proper operation ofthe automatic gain control circuitry. Other possible variations ofutilizing the differences of neighboring tones include obtaining$\begin{matrix}{\sum\limits_{k\quad = \quad {L\quad + \quad 1}}^{N}{\quad {{\left. H_{k} \middle| {- \left| \left. H_{k\quad - \quad L}\quad ||{}_{2}{/\quad \sum\limits_{k\quad = \quad 1}^{N}} \right.\quad \middle| H_{k}\quad  \middle| {}_{2}{.{or}} \right.} \right.}}}} & (8) \\{\sum\limits_{k\quad = \quad {L\quad + \quad 1}}^{N}\quad \left. ||{{Re}\left\{ H_{k} \right\} {\quad\left| {+ \left| {{Im}\left\{ H_{k} \right\}} \middle| {- \left| {{Re}\left\{ H_{k\quad - \quad L} \right\}} \middle| {- \left| {{Im}\left\{ H_{k\quad - \quad L} \right\}}||{/{\sum\limits_{k\quad = \quad 1}^{N}\quad {\left( \left| {{Re}\left\{ H_{k} \right\}} \middle| {+ \left| {{Im}\left\{ H_{k} \right\}} \right|} \right. \right).}}} \right.} \right.} \right.} \right.}} \right.} & (9)\end{matrix}$

[0039] The denominator of (9) can also be assumed to be a constant.These quantities can be used as a rough measure of delay spread. Themulti-path effect on the overall detection performance can also beestimated by observing the number of subcarriers whose signal strengthfalls below a certain threshold. Given the built-in, forward errorcorrection capability, this is a reliable measure of the multi-patheffect. Once the delay spread or multi-path effect is estimated, it canbe used together with other information such as the date rate, the RSSI,and the noise variance estimate to obtain a reasonable estimate for thebit or packet error rate of the current link.

[0040] A modem detector may also be used in accordance with theinvention to assess link quality. In particular, a detection qualitymeasure (DQM) can be observed within the modem. For example, thedetection quality is reflected in the magnitudes of the soft decisionscaptured at the Viterbi detector input, e.g., the average of1/[1+exp(|L_(i)|)], where L_(i) is the soft decision for the ith bit.These soft decisions can be used to estimate the bit error rate.

[0041] Since the functional relationship between such a DQM and the biterror rate or the packet error rate can be obtained empirically, the DQMcan drive the mode selection and/or the antenna selection.

[0042] Examination of the internal Viterbi detector parameters alsoprovides a useful measure of the detection quality. As an example, aconsistently small difference between the best survivor path metric andthat of the second best contender indicates that the Viterbi detectoroperates without much confidence and thus the decision quality is nothighly reliable.

[0043] A frequent disagreement among the surviving paths in making a bitdecision is another indication of a relatively poor packet receptionquality. If the detection quality is good, all or the overwhelmingmajority of the survivor paths will point to the same bit decision. Onthe other hand, when the Viterbi detector operates in a harsh linkcondition, the survivor paths will tend to dispute frequently in makingtheir bit decisions. No matter which method is adopted, the MAC layerfunctions must always verify the Receiver Address (RA) field in the MACheader to ensure that the packets are intended for the receiving stationunder consideration.

[0044] A MAC layer analyzer may also be used in accordance with anembodiment of the invention to assess link quality. The MAC layeranalyzer assesses link quality by relying upon MAC layer parameters. Onemethod applicable to WLAN is to examine the Retry Subfield in the MACheader of the received packet and observe the number of retriesattempted. As the number of retries on a given packet reaches a certainthreshold, the antenna connection or the diversity mode can be changedin hopes of establishing a better link. This approach can be combinedwith the CRC check result. A failed CRC check would indicate animpending attempt of another retry and thus can be used to acceleratethe decision making process. The problem here is, however, that with afailed CRC check, it would not be clear if the packet was intended forthe receiving station under question since the RA field could becontaminated with erroneous bits. One way to get around this difficultyis to assume that the probability of getting an error in the RA field isnegligible and simply treat the decoded RA as the true intended address.This assumption will be correct in most cases since the packet size willalmost always be very large compared to the RA field and the probabilityof an error in the RA field is considerably smaller than elsewhere inthe packet. The MAC layer parameters are quite convenient as the linkquality can be assessed independent of the data rate or multi-patheffects.

[0045] A particularly efficient way of implementing the proposed dynamicdiversity concept is to utilize both MAC and PHY layer parameters. Forexample, the receiver can rely on the inspection of the Retry Subfieldto sense degradation in the link quality and signal a transition to thefull diversity mode. On the other hand, the reverse transition from thefull diversity mode to the simpler antenna setting can be triggered whenthe RSS level increases by some prescribed amount (which could be adata-rate-dependent value).

[0046] When there is a user overwrite in favor of high performance orthe station is connected to a permanent power source, the dynamic modeselection feature can be disabled and the receiver can stay in the falldiversity mode. On the other hand, if the user desires the lowest powerconsumption, then the receiver can remain in the simpler diversity mode.

[0047] The invention utilizes a diversity configuration selector toselect an antenna whose receive path yields the larger SNR or signalpower. The SNR or signal strength measurement can take place during arelatively short preamble period at the beginning of the packet. Once acomparison is made, only the stronger antenna connection is maintainedfor the rest of the packet. To minimize power consumption, it is desiredto have only one receive path turned on during the listen periods, wherethe receiver is only monitoring the incoming signal level. Thedifficulty then is to determine the timing of a packet arrival to turnon both antenna connections. One way of handling this is to turn on theother antenna connection as soon as the arrival of a packet is detected.Once the selection is made based on RSSI measurements, the antenna witha lesser RSS can be disconnected.

[0048] Another method is to rely on the beacon packets that are releasedperiodically by the access point (AP) and addressed to every station inits network. Since the arrival times of the beacon packets are roughlyknown in advance, both antenna paths can be turned on in anticipation ofthese packets. Once the MAC layer verifies the beacon packet, theantenna selection can be made based on the RSSI measurements made duringthe beacon reception. Similarly, antenna selection can also be madebased on RSSI measurements during the reception of an acknowledgementpacket. This method will also work if the receiving station underconsideration also engages in transmission on a regular basis. Once thepacket is transmitted, the arrival time of the acknowledgement packetcan be predicted within a reasonable range.

[0049]FIG. 6 illustrates a dynamic diversity controller 600 utilized toimplement the techniques of the invention. The dynamic diversitycontroller 600 includes a link quality assessor 602. As discussed below,the link quality assessor 602 may include a signal strength analyzer, amodem detector, and/or a MAC layer analyzer to assess link quality andgenerate a link characterization value, which is passed to the diversityselection controller 604. The link characterization value or linkinformation can include the receiver-side link quality measure (RLQM)and the receive signal strength indicator (RSSI). Standard circuitry canbe utilized to generate this information

[0050] The diversity configuration selector 604 processes the linkcharacterization value to identify a diversity configuration, which isimplemented through a control signal or control signals generated by thediversity configuration selector 604. The link quality assessmentsdiscussed above are used individually or in combination to generate thelink characterization value.

[0051] As discussed above, the link quality assessor 602 may utilize avariety of signal assessment strategies. For example, the link qualityassessor may process time domain samples or frequency domain values. Inone embodiment, the link quality assessor includes N fixed frequencybins, where the k-th symbol transmission occupies the (k modulo N)-thfrequency bin. The link quality assessor 602 may also measure orthogonalfrequency division multiplexing (OFDM) coherence bandwidth to produce adelay spread estimate. OFDM coherence bandwidth may also be assessedfrom a frequency correlation function to produce a delay spreadestimate. OFDM coherence bandwidth may also be assessed from an overalldeviation of frequency response from an average value to produce a delayspread estimate. The link quality assessor can also be configured tomeasure the accumulated differences of immediately adjacent tones toproduce a delay spread estimate. Further, the number of subcarrierswhose signal strength falls below a threshold may be used to produce adelay spread estimate.

[0052] As previously indicated, the modem detector 812 of the linkquality assessor 602 may utilize a variety of strategies. For example,the modem detector 812 may be configured to measure magnitudes of softdecisions captured at the input of a Viterbi detector. The modemdetector can also measure internal Vierbi detector parameters. The modemdetector may also identify disagreement between surviving signal pathsin a Viterbi detector.

[0053] The MAC layer analyzer 814 of the link quality assessor 602 mayalso utilize a number of the previously discussed strategies. Forexample, the MAC layer analyzer 814 may examine MAC layer parameters toassess link quality. The MAC layer analyzer 814 can assess the qualityof the link using a MAC analysis that examines Wireless Local AreaNetwork (WLAN) retry sub-fields in a MAC header. The MAC layer analyzer814 can also assess the quality of the link using a MAC analysis thatexamines WLAN retry sub-fields in a MAC header and a CRC check result.In addition, the MAC analyzer 814 can examine MAC parameters and a modemdetector that examines physical (PHY) layer parameters.

[0054] The link characterization value is processed by the diversityconfiguration selector 604 according to one or more of the diversityselection techniques discussed above. That is, the diversityconfiguration selector 604 may utilize one or more of the strategiesdiscussed in connection with FIGS. 3-5.

[0055] The dynamic diversity controller 600 is connected to antennae andswitches. In particular, FIG. 6 illustrates a first antenna 606 and asecond antenna 608, respectively connected to switches 610 and 612. Theswitches 610 and 612 operate in response to a control signal from thediversity configuration selector 604. Amplifiers 614 and 616 preferablyprocess the outputs from the switches 610 and 612. The link qualityassessor 602 processes the amplifier output signals. An amplifier 618boosts the transmission signal.

[0056] During reception or listen periods, the diversity configurationselector 604 connects at least one switch 610 or 612 to the receive nodeR. While in full diversity, both switches 610 and 612 are connected toreceive nodes R. In the lower-power diversity mode, only one switch isconnected to a receive node R under the control of the diversityselection controller 604. For transmission, either switch (or possiblyboth switches) are closed to the transmit (T) position.

[0057]FIG. 7 illustrates a more efficient implementation of antennaswitching. There is only one transmission/receive switch 700. Fortransmission, the switch 700 moves to the T position and only antenna606 is used. During reception or the listening mode the switch is set atR. Thus, ostensibly both paths are connected during reception or listenperiods. However, to effectively achieve the desired antennaswitching/selection during reception, a control signal simply turns thepower up/down (or on/off) for the entire radio frequency (RF) and analogpath including analog-to-digital converters (not shown). This eliminatesthe need for an extra switch and avoids the signal loss associated withit.

[0058]FIG. 8 illustrates an embodiment of the dynamic diversitycontroller 600. In this embodiment, the dynamic diversity controller 600includes a control circuit (e.g., a microprocessor) 800 connected to aset of input and output devices 802 via a bus 804. A memory module(e.g., primary and/or secondary memory) 806 is also connected to the bus804. A dynamic diversity control module 808 is stored in the memory 806.The dynamic diversity control module 808 includes a set of executableinstructions to implement the operations of the link quality assessor602 and the diversity configuration selector 604. In one embodiment, thelink quality assessor 602 includes a signal strength analyzer 810 toimplement the signal strength assessments techniques discussed above.The link quality assessor 602 also includes a modem detector 812 toimplement the modem detection techniques discussed above. In addition, aMAC layer analyzer 814 is used to implement the MAC analysis techniquesdiscussed above. The diversity configuration selector 604 implements oneor more of the diversity selection operations discussed above inconnection with FIGS. 3-5.

[0059] The configuration of FIG. 8 is exemplary. The dynamic diversitycontroller 600 may also be implemented as a hardwired circuit, anApplication Specific Integrated Circuit (ASIC), a programmable logicdevice, and the like.

[0060] The foregoing description, for purposes of explanation, usedspecific nomenclature to provide a thorough understanding of theinvention. However, it will be apparent to one skilled in the art thatspecific details are not required in order to practice the invention.Thus, the foregoing descriptions of specific embodiments of theinvention are presented for purposes of illustration and description.They are not intended to be exhaustive or to limit the invention to theprecise forms disclosed; obviously, many modifications and variationsare possible in view of the above teachings. The embodiments were chosenand described in order to best explain the principles of the inventionand its practical applications, they thereby enable others skilled inthe art to best utilize the invention and various embodiments withvarious modifications as are suited to the particular use contemplated.It is intended that the following claims and their equivalents definethe scope of the invention.

In the claims:
 1. An apparatus for dynamic diversity signal receptionbased upon receiver-side link quality assessment, comprising: two ormore antennae; at least one switch connected to said two or moreantennae; and a dynamic diversity control module connected to said atleast one switch, said dynamic diversity control module including a linkquality assessor to assess a received signal and generate a linkcharacterization value, and a diversity configuration selector,responsive to said link characterization value, to selectively activatesaid at least one switch to implement a dynamic diversity configuration.2. The apparatus of claim 1 wherein said link quality assessor processessaid received signal as time-domain samples.
 3. The apparatus of claim 1wherein said link quality assessor processes said received signal asfrequency-domain samples.
 4. The apparatus of claim 1 wherein said linkquality assessor processes said received signal as frequency-domainsamples, said link quality assessor including N fixed frequency bins,wherein the k-th symbol transmission occupies the (k modulo N)-thfrequency bin.
 5. The apparatus of claim 1 wherein said link qualityassessor includes a signal strength analyzer.
 6. The apparatus of claim1 wherein said link quality assessor measures orthogonal frequencydivision multiplexing (OFDM) coherence bandwidth to produce a delayspread estimate.
 7. The apparatus of claim 1 wherein said link qualityassessor measures orthogonal frequency division multiplexing coherencebandwidth from a frequency correlation function to produce a delayspread estimate.
 8. The apparatus of claim 1 wherein said link qualityassessor measures orthogonal frequency division multiplexing coherencebandwidth from an overall deviation of frequency response from anaverage value to produce a delay spread estimate.
 9. The apparatus ofclaim 1 wherein said link quality assessor measures the accumulateddifferences of adjacent tones to produce a delay spread estimate. 10.The apparatus of claim 1 wherein said link quality assessor observes thenumber of sub-carriers whose signal strength falls below a threshold toproduce a delay spread estimate.
 11. The apparatus of claim 1 whereinsaid link quality assessor includes a modem detector to measuremagnitudes of soft decisions captured at the input of a Viterbidetector.
 12. The apparatus of claim 1 wherein said link qualityassessor includes a modem detector to measure internal Viterbi detectorparameters.
 13. The apparatus of claim 1 wherein said link qualityassessor includes a modem detector to identify disagreement betweensurviving signal paths in a Viterbi detector.
 14. The apparatus of claim1 wherein said link quality assessor includes a MAC layer analyzer toexamine MAC layer parameters to assess link quality.
 15. The apparatusof claim 1 wherein said link quality assessor includes a MAC layeranalyzer to assess the quality of the link using a MAC analysis thatexamines Wireless Local Area Network (WLAN) retry sub-fields in a MACheader.
 16. The apparatus of claim 1 wherein said link quality assessorincludes a MAC layer analyzer to assess the quality of the link using aMAC analysis that examines Wireless Local Area Network (WLAN) retrysub-fields in a MAC header and a CRC check result.
 17. The apparatus ofclaim 1 wherein said link quality assessor includes a MAC analyzer thatexamines MAC parameters and a modem detector that examines physical(PHY) layer parameters.
 18. The apparatus of claim 1 wherein saiddiversity configuration selector generates control signals for said atleast one switch to selectively implement switched diversity and fulldiversity modes.
 19. The apparatus of claim 1 wherein said diversityconfiguration selector generates control signals for said at least oneswitch to selectively transition from no diversity to full diversityconfigurations.
 20. The apparatus of claim 1 wherein said diversityconfiguration selector receives a receiver-side link quality measure anda receive signal strength indicator from said link quality assessor. 21.The apparatus of claim 1 wherein only one antenna is turned on duringsignal listen periods.
 22. The apparatus of claim 1 wherein said twoantennae are turned on automatically at the beginning of each receivedpacket.
 23. The apparatus of claim 1 wherein diversity configurationselection is made at the end of a preamble period of each receivedpacket.
 24. The apparatus of claim 1 wherein link quality assessment isbased on examination of beacon packets released by a WLAN access point.25. The apparatus of claim 1 wherein link quality assessment is based onexamination of acknowledgment packets released by a WLAN transmitter.26. An apparatus for dynamic diversity signal reception based uponreceiver-side link quality assessments, comprising: two antennae; asingle switch connected to one of said two antennae; and a dynamicdiversity control module connected to said single switch, said dynamicdiversity control module including: a link quality assessor to assesslink information received from said two antennae and generate a linkcharacterization value, and a diversity configuration selector,responsive to said link characterization value, to selectively activatesaid switch to implement a dynamic diversity configuration.
 27. Theapparatus of claim 26 wherein said dynamic diversity control moduleturns power on and off entire radio frequency and analog signal paths.28. An apparatus to facilitate dynamic diversity signal reception,comprising: a bus; a control circuit connected to said bus; input andoutput devices connected to said bus to route received signalinformation and transmit a control signal; and a dynamic diversitycontrol module connected to said bus, said dynamic diversity controlmodule including a link quality assessor and a diversity configurationselector.
 29. The apparatus of claim 28 wherein said link qualityassessor includes a signal strength analyzer to process said receivedsignal information and generate a link characterization value that isprocessed by said diversity configuration selector to generate a controlsignal to facilitate dynamic diversity signal reception.
 30. Theapparatus of claim 28 wherein said link quality assessor includes amodem detector to process said received signal information and generatea link characterization value that is processed by said diversityconfiguration selector to generate a control signal to facilitatedynamic diversity signal reception.
 31. The apparatus of claim 28wherein said link quality assessor includes a medium access control(MAC) layer analyzer to process said received signal information andgenerate a link characterization value that is processed by saiddiversity configuration selector to generate a control signal tofacilitate dynamic diversity signal reception.
 32. The apparatus ofclaim 28 wherein said diversity configuration selector facilitatesswitched diversity and full diversity modes.
 33. The apparatus of claim28 wherein said diversity configuration selector facilitates selectivetransitions from no diversity to full diversity configurations.
 34. Amethod of dynamic diversity selection based upon receiver-side linkquality assessments, comprising: receiving a wireless signal at awireless mobile device; assessing link quality using a techniqueselected from a signal strength analysis, a modem detection analysis,and a medium access control (MAC) analysis; and selecting an antennadiversity configuration based upon said assessing.
 35. The method ofclaim 34 wherein assessing includes assessing link quality using asignal strength analysis.
 36. The method of claim 34 wherein assessingincludes assessing link quality by measuring orthogonal frequencydivision multiplexing coherence bandwidth.
 37. The method of claim 34wherein assessing includes measuring orthogonal frequency divisionmultiplexing coherence bandwidth from a frequency correlation function.38. The method of claim 34 wherein assessing includes measuringorthogonal frequency division multiplexing coherence bandwidth from anoverall deviation of frequency response from an average value.
 39. Theapparatus of claim 34 wherein assessing includes measuring theaccumulated differences of - adjacent tones.
 40. The apparatus of claim34 wherein assessing includes observing the number of subcarriers whosesignal strength falls below a threshold.
 41. The method of claim 34wherein assessing includes assessing link quality using a modemdetection analysis measuring magnitudes of soft decisions captured atthe input of a Viterbi detector.
 42. The method of claim 34 whereinassessing includes assessing link quality using a modem detectionanalysis measuring internal Viterbi detector parameters.
 43. The methodof claim 34 wherein assessing includes assessing link quality using amodem detection analysis identifying disagreement between survivingsignal paths in a Viterbi detector.
 44. The method of claim 34 whereinassessing includes assessing link quality using a MAC analysis thatexamines MAC layer parameters to assess link quality.
 45. The method ofclaim 34 wherein assessing includes assessing link quality using a MACanalysis that examines Wireless Local Area Network (WLAN) retrysub-fields in a MAC header.
 46. The method of claim 34 wherein assessingincludes assessing link quality using a MAC analysis that examinesWireless Local Area Network (WLAN) retry sub-fields in a MAC header anda CRC check result
 47. The method of claim 34 wherein assessing includesassessing link quality using a MAC analysis that examines MAC parametersand a modem detector that examines physical (PHY) layer parameters. 48.The method of claim 34 wherein selecting includes choosing a fulldiversity mode when said link quality falls below a full diversity modethreshold value.
 49. The method of claim 48 wherein selecting includesidentifying when said link quality rises above a full diversity modetransition threshold value.
 50. The method of claim 49 furthercomprising identifying the larger of a first antenna receive signalstrength indicator and a second antenna receive signal strengthindicator.
 51. The method of claim 50 further comprising selecting afirst antenna single static connection configuration when said firstantenna receive signal strength indicator is larger than said secondantenna receive signal strength indicator.
 52. The method of claim 51further comprising maintaining said first antenna single staticconnection configuration while a first antenna receiver-side linkquality measure value is above a threshold value.
 53. The method ofclaim 50 further comprising selecting a second antenna single staticconnection configuration when said second antenna receive signalstrength indicator is larger than said first antenna receive signalstrength indicator.
 54. The method of claim 53 further comprisingmaintaining said second antenna single static connection configurationwhile a second antenna receiver-side link quality measure value is abovea threshold value.